Galaxies

Quasars and Active Galaxies

What is the unified model of active galactic nuclei?

After decades of studying AGNs, astronomers have put together a single, unified model that might explain why all AGNs look the way they do. Basically, all AGNs have the same basic structure: they have a QSO sitting in the middle of a galaxy. Depending on whether we are looking down the barrel of a super-energetic jet, or right into the side of the gas torus, or at some angle in between, the QSO will have a different spectroscopic signature from our point of view. Furthermore, the QSO host galaxy could be spiral, elliptical, or peculiar, and we could be seeing the QSO through a screen of interstellar dust, or lots of gas, or a lot of stars of differing colors and luminosities. The host galaxy would therefore contribute its own components to the spectroscopic signature of an AGN. Depending on what is in the way, and what part of the QSO we can see, each AGN looks unique. In actuality, all AGNs are basically the same.